Method of manufacturing multilayer thin film pattern and display device

ABSTRACT

A method of manufacturing a multilayer thin film pattern includes forming a metal film over a substrate, forming a second thin film over the metal film, forming a resist pattern over the second thin film, etching the second thin film using the resist pattern as a mask, transforming the resist pattern using an organic solvent or a RELACS agent to cover an edge face of the etched second thin film and etching the metal film while the edge face of the second thin film is covered with the resist pattern.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multilayer thin film pattern and amethod of manufacturing a display device.

2. Description of Related Art

For liquid crystal displays, there are for example a transmissive type,a reflective type and a transflective type liquid crystal display (forexample see Japanese Unexamined Patent Application Publication No.11-101992). A transmissive liquid crystal display shows an image by abacklight disposed at its back. A reflective liquid crystal displayshows an image by its surrounding light reflected on a reflector surfacewhich is disposed to a substrate. Therefore, the reflective liquidcrystal display includes a pixel electrode for reflecting light, thatis, a reflective pixel electrode. A transflective liquid crystal displaytransmits a part of light and reflects a part of light. In thetransflective liquid crystal display, a TFT array substrate has both atransmissive pixel electrode (transmissive electrode) and a reflectivepixel electrode.

In the transmissive liquid crystal display, it is usually required thatboth a pixel electrode over a TFT array substrate and an opposingelectrode over a color filter substrate are transparent, and atransparent conductive film, such as ITO, is used for both of them as anelectrode material. Accordingly, at the time of the alternating currentdrive of a liquid crystal, the abovementioned pixel electrode and theopposing electrode can apply positive and negative voltages to theliquid crystal under almost the same conditions. On the other hand, inthe transflective liquid crystal display, a metal film such as Al isused as a reflective pixel electrode (reflective electrode). Therefore,display flicker and liquid crystal image sticking are generatedaccording to the driving condition due to a work function differencewith the transparent conductive film which is the opposing electrode.

As a countermeasure for such flicker and image sticking, a technique forforming a transparent conductive film made of the same material as anopposing electrode over a metal of a reflective electrode is disclosedin Japanese Unexamined Patent Application Publication Nos. 2003-255378and 2005-275323. In Japanese Unexamined Patent Application PublicationNo. 2005-275323, the metal film of the reflective electrode and thetransparent conductive film over the reflective electrode arecollectively wet etched using the same etchant and the same maskpattern. This enables to form the reflective electrode and thetransparent conductive film which has the same pattern shape as thereflective electrode.

Moreover, in the transflective liquid crystal display, both processes offorming the transmissive electrode and forming the reflective electrodeare included. Therefore, in the transflective liquid crystal display,there are more photolithography processes required compared with thetransmissive liquid crystal display and the reflective liquid crystaldisplay. In order to reduce the number of photolithography processes, atechnique of devising the photolithography is disclosed in JapaneseUnexamined Patent Application Publication No. 2005-215277. In JapaneseUnexamined Patent Application Publication No. 2005-215277, using a graytone or a halftone exposure technique for the photolithography, the filmthickness of the resist (photosensitive resin) pattern is changed foreach part. By the resist pattern with different film thicknesses, thetransmissive electrode and the reflective electrode are processed in onephotolithography process.

However, when the metal film and the transparent conductive film formedthereover are collectively wet etched by the technique disclosed inJapanese Unexamined Patent Application No. 2005-275323, the transparentconductive film may hang over the metal film edge face and remain as aprotruding shape (an overhang). FIGS. 8A to 8D are cross-sectionaldiagrams schematically showing a manufacturing process of a TFT arraysubstrate in a transflective liquid crystal display according toJapanese Unexamined Patent Application Publication No. 2005-275323. InFIG. 8A, a first transparent conductive film 2 is formed and patternedover an interlayer insulating film 1 which is formed above a TFT (notshown), a scanning signal line (not shown) and a display signal line(not shown). Next, in FIG. 8B, a metal film 3 as a reflective electrodeis formed to cover the first transparent conductive film 2. Then, asecond transparent conductive film 4 is formed to prevent flicker andimage sticking. Subsequently, a resist pattern 5 of desired shape isformed over the second transparent conductive film 4. The metal film 3and the second transparent conductive film 4 are collectively wet etchedwith the resist pattern 5 being formed thereover, as shown in FIG. 8C.After that, the resist pattern 5 is removed and it becomes theconfiguration as shown in FIG. 8D.

When a multilayer thin film pattern is formed by the above method, thesecond transparent conductive film 4 which is the upper layer is formedto be protruding shape projected from the pattern end of the lower layermetal film 3. Especially when using isotropic etching such as wetetching, the protruding shape of the second transparent conductive film4 is likely to appear. FIG. 9 is a partial enlarged diagram showing thestate during the collective wet etching process of the secondtransparent conductive film 4 and the metal film 3. In isotropicetching, etching proceeds to the vertical and the horizontal directionsat the same time. That is, while the etching of the second transparentconductive film 4 and the metal film 3 proceeds in the direction of filmthickness, the etching also proceeds in the direction perpendicular tofilm thickness (side etch). By the side etch, as shown in FIG. 9, ahollow 6 is formed between an etching surface 7 of the metal film 3 andthe resist pattern 5 surface during the etching. Since the etchingproceeds also from this hollow 6, the protrusion is likely to begenerated. Furthermore, generally the etching rate of the metal film 3is faster than that of the second transparent conductive film 4, thusthe metal film 3 is more likely to be side etched than the secondtransparent conductive film 4. Consequently, the second transparentconductive film 4 projects to form the protruding shape.

Thus, if the protrusion is formed in the edge face of the multilayerthin film, during the process of rubbing substrates such as a rubbingprocess in the next panel manufacturing process, the protruding portioncomes off to be a cause of generating a contamination particle. Then,the piece of the separated film could lead to a short-out betweenadjacent pixels or between a pixel electrode and an opposing electrode,thereby causing a display failure. Moreover, when the edge face of themultilayer film pattern is covered with a covering film, continuity ofthe covering film is broken at the protruding portion. If the coveringfilm is a protective insulating film, an insulation failure occurs inthe portion of the discontinuity. If the covering film is a conductivefilm, an electric connection failure occurs in the portion of thediscontinuity. As the definition of display devices advances higher inthe future, pixel size and space between adjacent pixels will becomesmaller. Thus the process to more effectively prevent from generatingthe projection is required.

Moreover, in Japanese Unexamined Patent Application Publication No.2005-215277, the resist pattern with different film thicknesses is usedto form the transparent electrode and the reflective electrode. Thethinner part of the resist pattern with different film thicknesses isremoved by ashing. Oxygen plasma treatment is usually used for thisashing. However, according to the method of Japanese Unexamined PatentApplication Publication No. 2005-215277, the ashing is performed whilethe transparent conductive film is exposed to the surface, and thusabnormal electrical discharge may arise. By abnormal electricaldischarge, not only the transparent conductive film but the interlayerinsulating film provided thereunder is also damaged. Furthermore, it maycause a failure such as a disconnection of the line provided in thelower layer.

The present invention is made in order to solve the above problems andan object of this invention is to provide a manufacturing method of amultilayer thin film pattern and a display device that can easily obtaina pattern with a desired shape.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided amethod of manufacturing a multilayer thin film pattern that includesforming a first thin film (for example the metal film 3 in theembodiments) over a substrate, forming a second thin film (for examplethe second transparent conductive film 4 in the embodiments) over thefirst thin film, forming a resist pattern over the second thin film,etching the second thin film using the resist pattern as a mask,transforming the resist pattern using an organic solvent or a RELACSagent to cover an edge face of the etched second thin film and etchingthe first thin film while the edge face of the second thin film iscovered with the resist pattern.

According to another aspect of the present invention, there is provideda method of manufacturing a multilayer thin film pattern that includesforming an interlayer insulating film over a substrate, forming aconductive thin film over the interlayer insulating film, forming a thinfilm of one layer or more over the conductive thin film, forming aresist pattern having different film thicknesses by a multi-toneexposure over the thin film of one layer or more, etching the thin filmof one layer or more and the conductive thin film using the resistpattern having different film thicknesses as a mask to expose theinterlayer insulating film, ashing the resist pattern having differentfilm thicknesses to remove a thin film part of the resist pattern andetching at least one layer of the thin film of one layer or more usingthe resist pattern without the thin film part as a mask.

The present invention is able to provide the manufacturing method of themultilayer thin film pattern and the display device which can easilyobtain the pattern of desired shape.

The above and other objects and features and advantages of the presentinvention will become more fully understood from the detaileddescription given hereinbelow and the accompanying drawings which aregiven by way of illustration only, and thus are not to be considered aslimiting the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure of an electrode substrate of a liquid crystaldisplay according to the present invention;

FIG. 2A is a plane view schematically showing the pixel structure of atransflective liquid crystal display according to the present invention;

FIG. 2B is a cross-sectional diagram taken along the line IIB-IIB ofFIG. 2A;

FIGS. 3A to 3G schematically show a manufacturing process of amultilayer thin film pattern according to a first embodiment;

FIGS. 4A to 4G schematically show a manufacturing process of amultilayer thin film pattern according to a third embodiment;

FIGS. 5A to 5I schematically show a manufacturing process of amultilayer thin film pattern according to a fourth embodiment;

FIGS. 6A to 6D schematically show a manufacturing process of amultilayer thin film pattern according to a fifth embodiment;

FIGS. 7A to 7D schematically show a manufacturing process of amultilayer thin film pattern according to a sixth embodiment;

FIGS. 8A to 8D schematically show a manufacturing process of amultilayer thin film pattern according to a related art; and

FIG. 9 is a partial enlarged diagram showing an etching process of amultilayer thin film pattern according to a related art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Firstly, a display device according to the present invention isexplained with reference to FIG. 1. FIG. 1 is a front view showing thestructure of an electrode substrate used for a liquid crystal display.Although the display device according to the present invention isexplained with a liquid crystal display as an example, it is onlyillustrative and a flat panel display or the like such as an organic ELdisplay may be used. The overall structure of this liquid crystaldisplay is common to the first to the sixth embodiments described below.

The display device according to the present invention includes anelectrode substrate 10. To the electrode substrate 10, a display area 11and a frame area 12 surrounding the display area 11 are provided. Aplurality of scan signal lines 13 and a plurality of display signallines 14 are formed in the display area 41. The plurality of scanningsignal lines 13 are provided in parallel. Similarly, the plurality ofdisplay signal lines 14 are formed in parallel. The scanning signal line13 and the display signal line 14 are formed to cross each other. Thescanning signal line 13 and the display signal line 14 are orthogonal.Moreover, an area surrounded by adjacent scan signal lines 13 anddisplay signal lines 14 is a pixel 17. Therefore, in the electrodesubstrate 10, the pixels 17 are arranged in matrix. As described above,the electrode substrate 10 is a TFT array substrate.

Furthermore, a scanning signal driving circuit 15 and a display signaldriving circuit 16 are provided in the frame area 12 of the electrodesubstrate 10. The scanning signal lines 13 are extended from the displayarea 11 to the frame area 12. Then the scanning signal lines 13 areconnected to the scanning signal driving circuit 15 at the end part ofthe electrode substrate 10. The display signal lines 14 are alsoextended from the display area 11 to the frame area 12. Then the displaysignal lines 13 are connected to the display signal driving circuit 16at the end part of the electrode substrate 10. An external wiring 18 isconnected near the scanning signal driving circuit 15. Furthermore, anexternal wiring 19 is connected near the display signal driving circuit16. The external wirings 18 and 19 are wiring boards such as FPC(Flexible Printed Circuit).

Various signals from outside are supplied to the scanning signal drivingcircuit 15 and the display signal driving circuit 16 through theexternal wirings 18 and 19. The scanning signal driving circuit 15supplies a scanning signal to the scanning signal line 13 based on acontrol signal from outside. By this scanning signal, the scanningsignal lines 13 are selected sequentially. The display signal drivingcircuit 16 supplies a display signal to the display signal line 14according to the control signal and display data from outside. Thisenables to supply a display voltage corresponding to the display data toeach pixel 17. Note that the scanning signal driving circuit 15 and thedisplay signal driving circuit 16 are not limited to the structuredisposed over the electrode substrate 10. For example, the drivingcircuits may be connected by TCP (Tape Carrier Package).

At least one TFT 20 is formed in the pixel 17. An interlayer insulatingfilm is formed over the TFT 20. The TFT 20 is disposed near theintersection of the display signal line 14 and the scanning signal line13. The TFT 20 and the pixel are connected through a contact holeprovided in the interlayer insulating film. For example, this TFT 20supplies a display voltage to a pixel electrode. That is, the TFT 20,which is a switching device, is turned on by a scanning signal from thescanning signal line 13. This enables to apply the display voltage tothe pixel electrode connected to a drain electrode of the TFT 20 fromthe display signal line 14. Then, an electric field according to thedisplay voltage is generated between the pixel electrode and an opposingelectrode. Note that an alignment layer (not shown) is formed over thesurface of the electrode substrate 10.

Here, the structure of the pixel 17 is explained in detail withreference to FIGS. 2A and 2B. In this example, the pixel structure of atransflective liquid crystal display which is an example of the displaydevice according to the present invention is explained. FIG. 2A is aplane view schematically showing the pixel structure of thetransflective liquid crystal display according to the present invention.FIG. 2B is a cross-sectional diagram taken along the line IIB-IIB ofFIG. 2A. Note that in FIG. 2A, only the pixel structure on the side ofthe electrode substrate 10 is illustrated. In FIG. 2B, along with thecross-sectional diagram taken along the line IIB-IIB of the electrodesubstrate 10, the cross-sectional structure on the side of the opposingsubstrate corresponding to the IIB-IIB cross section of the electrodesubstrate 10 is also illustrated. Although an example of using achannel-etch type inverted staggered TFT is illustrated in FIGS. 2A and2B, it is not limited to this. For example, it may be an etch-stopper ora top-gate type TFT.

In FIG. 2A, the plurality of scanning signal lines (gate lines) 13 areformed in the vertical direction. The plurality of display signal lines(source lines) 14 are formed in the horizontal direction. The areasurrounded by the adjacent scanning signal lines 13 and the displaysignal lines 14 is the pixel 17. Over a substrate 61 of the electrodesubstrate 10, the scanning signal line 13, a gate electrode 62, and acommon capacitor electrode 63 are formed in the same layer. Thesubstrate 61 is a transparent insulating substrate such as glass andplastic. The scanning signal line 13 is connected to the gate electrode62 outside the TFT 20. A gate insulating film 64 is formed to cover thegate electrode 62, the scanning signal line 13 and the common capacitorelectrode 63, as shown in FIG. 2B.

A semiconductor layer 65 of the TFT 20 is formed over the gateinsulating film 64. The semiconductor layer 65 is disposed near theintersection of the scanning signal line 13 and the display signal line14. Specifically, the semiconductor layer 65 is provided opposite to thegate electrode 62 with the gate insulating film 64 interposedtherebetween. The semiconductor layer 65 is formed of an intrinsicamorphous semiconductor layer (an i layer) 65 a and an n-type amorphoussemiconductor layer (an n layer) 65 b. The i layer 65 a is provided overthe gate insulating film 64 and has substantially the same size as thegate electrode 62. The n layer 65 b is provided over the i layer 65 a.The n layer 65 b corresponding to between a source electrode 66 and adrain electrode 67 which are described later is removed by a backchannel etching. That is, the n layer 65 b is formed between the sourceelectrode 66 and the i layer 65 a and between the drain electrode 67 andthe i layer 65 a.

Furthermore, the source electrode 66 and the drain electrode 67 areprovided over the gate insulating film 64 and respectively connectedwith the n layer 65 b of the semiconductor layer 65. The sourceelectrode 66 is connected with the display signal line 14 outside theTFT 20. The drain electrode 67 is extended over the common capacitorelectrode 63. For the drain electrode 67, the portion opposed to thecommon capacitor electrode 63 functions as a capacitor electrode forforming an additional capacitance of each pixel. A storage capacitor isformed by this capacitor electrode of the drain electrode 67, the commoncapacitor electrode 63 placed opposite, and the gate insulating film 64interposed therebetween. Therefore, the gate insulating film 64 over thecommon capacitor electrode 63 functions as a capacitor dielectric filmof the storage capacitor. The common capacitor electrode 63 is disposedbetween adjacent scanning signal lines 13. The common capacitorelectrodes 63 are connected between the adjacent pixels 17 to form acommon capacitor line as shown in FIG. 2A. Within the pixel 17, thecommon capacitor line is formed widely to be the common capacitorelectrode 63. The width of the common capacitor line is narrow in theportion intersecting the display signal line 14 so as to reduceparasitic capacitance. The common capacitor line is parallel to thescanning signal line 13.

An interlayer insulating film 68 is formed to cover the source electrode66 and the drain electrode 67. Over the interlayer insulating film 68,an interlayer insulating film 1 such as an organic planarizing film isprovided. A contact hole 69 which penetrates the interlayer insulatingfilms 1 and 68 is formed over the drain electrode 67. A pixel electrode70 is provided to connect to the drain electrode 67 through this contacthole 69. A first transparent conductive film 2 is formed in atransmissive area 9 and a reflective area 8 as the pixel electrode 70.Moreover, a metal film 3 is further formed in the reflective area 8 ofthe pixel electrode 70 over the first transparent conductive film 2.Therefore, the portion provided with the metal film 3 in the pixel 17 isto be the reflective area 8. The pixel 17 other than the reflective area8 is to be the transmissive area 9. The metal film 3 is disposed overthe common capacitor electrode 63. That is, in the reflective area 8, astorage capacitor is provided under the metal film 3. Note that althougha second transparent conductive film 4 may be further stacked over themetal film 3 to prevent image sticking, it is not shown in FIG. 2B.

An alignment layer 72 is formed to the surface of the electrodesubstrate 10 to cover the pixel electrode 70. Note that in thereflective area 8, an uneven portion 71 is provided in order to improvethe display properties of reflection mode. The uneven pattern is formedto the surface of the interlayer insulating film 1 in the uneven portion71. Then, in the uneven portion 71, the metal film 3 formed thereover isalso uneven to conform to the uneven pattern of the interlayerinsulating film 1.

Furthermore, an opposing substrate 50 is disposed opposite to theelectrode substrate 10. The opposing substrate 50 is for example a colorfilter substrate and is disposed to the visible side. A color filter 53,a black matrix (BM) 52, an opposing electrode 54, an alignment layer 72and so on are formed to the opposing substrate 50.

Specifically, to the surface of the substrate 51 opposing to theelectrode substrate 10, the black matrix 52 is formed. The black matrix52 is made of pigment or metal such as chromium and blocks light. Theblack matrix 52 is provided in the area opposed to the scanning signalline 13 and the display signal line 14. Then, the color filter 53 madefrom pigment or dye is formed to fill the area surrounded by the blackmatrix 52. The color filter 53 is disposed opposite to the pixelelectrode 70. The color filter 53 is a colored layer of R (red), G(green), and B (blue), for example. Furthermore, the opposing electrode54 is formed substantially all over the display area 11 to cover theblack matrix 52 and the color filter 53. Moreover, the alignment layer72 is stacked to the surface of the opposing substrate 50. Note that theopposing electrode 54 may be disposed to the electrode substrate 10side.

Then, a liquid crystal layer 73 is held between the electrode substrate10 and the opposing substrate 50. That is, liquid crystal is filled inbetween the electrode substrate 10 and the opposing substrate 50.Furthermore, a polarizing plate and a retardation film, etc. areprovided to the surface outside of the electrode substrate 10 and theopposing substrate 50. Moreover, a back light unit or the like is placedto the non-visible side of the liquid crystal display panel.

The liquid crystal is driven by the electric field between the pixelelectrode 70 and the opposing electrode 54. That is, an alignmentdirection of the liquid crystal between the substrates changes. Thischanges the polarization state of a light passing through the liquidcrystal layer 73. To be more specific, the light that has passed thepolarizing plate and has become a linearly polarized light changes itspolarization state by the liquid crystal layer 73. More specifically,the light from the backlight unit becomes a linearly polarized light bythe polarizing plate provided to the electrode substrate 10 side.Further, by the linearly polarized light passing through the liquidcrystal layer 73, the polarization state changes.

Accordingly, the amount of light passing through the polarizing plate ofthe opposing substrate 50 side varies according to the polarizationstate. More specifically, among transmitted light transmitting from thebacklight unit through the liquid crystal panel, the amount of lightpassing through the polarizing plate of the visible side varies. Thealignment direction of the liquid crystal varies according to theapplied display voltage. Therefore, by controlling the display voltage,the amount of light passing through the polarizing plate of the visibleside can be changed. That is, by varying the display voltage by eachpixel, a desired image can be displayed.

First Embodiment

Next, a manufacturing method of a multilayer thin film pattern accordingto a first embodiment is explained with reference to FIGS. 3A to 3G.FIGS. 3A to 3G are cross-sectional diagrams schematically showing themanufacturing process of the multilayer thin film pattern according tothe first embodiment. In this embodiment, although the manufacturingmethod of a reflective electrode and a transmissive electrode in a pixelelectrode of a transflective liquid crystal display is described as apreferred example of a multilayer thin film pattern and a displaydevice, it is not limited to this. Various multilayer thin film patternsand display devices can be formed by changing thin films for forming themultilayer thin film variously.

Firstly, in FIGS. 3A to 3G, as with FIGS. 8A to 8D, the interlayerinsulating film 1 such as an organic planarizing film is formed abovethe TFT 20, the scanning signal line 13 and the display signal line 14,as shown in FIGS. 2A and 2B. In FIGS. 3A to 3G, the part below theinterlayer insulating film 1 is omitted. In FIG. 3A, the firsttransparent conductive film 2, the metal film 3 to be a reflectiveelectrode, and the second transparent conductive film 4 for preventingimage sticking are deposited in order over the interlayer insulatingfilm 1. Al or an alloy mainly using Al, for example, is used for themetal film 3. Moreover, the first transparent conductive film 2 and thesecond transparent conductive film 4 are transparent conductive filmssuch as ITO and ITZO. Then, a resist pattern 5 of desired planar shapeis formed by photolithography over the second transparent conductivefilm 4.

Next, in FIG. 3B, the second transparent conductive film 4 isselectively etched until its edge is retracted under the resist pattern5. In this process, isotropic etching such as wet etching can be used.At this time, a retracting amount (side etch amount) 41 of the secondtransparent conductive film 4 from the edge face of the resist pattern 5by side etch shall be more than the side etch amount of the metal film3, which is described later. Here, only as a guide, the side etch amount41 shall be approximately more than twice the film thickness of themetal film 3.

Next, the resist pattern 5 is transformed by a reflow of the resistusing an organic solvent so that the resist pattern 5 covers the edgeface of the second transparent conductive film 4. For example, byexposing the resist pattern 5 to organic solvent atmosphere under lowtemperature of about 20 to 35 degrees Celsius, the resist pattern 5 istransformed largely in a short time. This enables to protect the entiresecond transparent conductive film 4 by the resist pattern 5, as shownin FIG. 3C. The transformation of the resist using the organic solventis disclosed in Kido, S. et al. “Late-News Paper: A 14-in. LCD PanelFormed Using New 4-Mask Technology with Chemical Re-Flow Technique”, SIDInternational Symposium Digest of Technical Papers, 2006. pp. 1650-1653.

Then, in FIG. 3D, isotropic etching of the metal film 3 is selectivelycarried out. For example, wet etching can be used. Even a small amountof the remaining metal film 3 will have a harmful effect on productperformance. Thus the metal film 3 must be sufficiently over etched.Therefore, in consideration of the variation in etching and thehomogeneity, the etching process corresponding about 1.5 to the 2 timesof the film thickness of the metal film 3 is performed. At this time, aretracting amount (side etch amount) 31 of the metal film 3 from theedge face of the resist pattern 5 by side etch is about 1.5 to 2 timesof the film thickness of the metal film 3. That is, the retractingamount 31 of the metal film 3 becomes smaller than the retracting amount41 of the second transparent conductive film 4. Consequently, the bottomsurface of the second transparent conductive film 4 is not exposedduring the etching process of the metal film 3, thereby enabling toprevent from generating the protruding portion by the second transparentconductive film 4. Furthermore, as with FIG. 3C, the resist pattern 5 istransformed again by the reflow of the resist using an organic solventso that the resist pattern 5 covers the edge face of the metal film 3.This enables to protect the second transparent conductive film 4 and themetal film 3 entirely by the resist pattern 5, as shown in FIG. 3E.

After that, in FIG. 3F, the first transparent conductive film 2 isetched. At this time, the first transparent conductive film 2 is etchedin such a way that a retracting amount 21 of the first transparentconductive film 2 from the edge face of the resist pattern 5 becomesless than the retracting amount 31 of the metal film 3. This enables themetal film 3 not to project from the edge face of the first transparentconductive film 2, thereby preventing from generating the protrudingportion. Here, wet etching can be used, for example.

Lastly, when the resist pattern 5 is removed, the multilayer thin filmpattern without the protruding portion can be obtained as shown in FIG.3G.

As described above, in this embodiment, using the resist pattern 5 as amask, isotropic etching is performed to the second transparentconductive film 4 formed below the mask. At this time, the secondtransparent conductive film 4 is selectively etched until its retractingamount 41 becomes more than twice the film thickness of the metal film3. Then, the resist pattern 5 is transformed by the reflow of the resistusing an organic solvent so that the resist pattern 5 covers the edgeface of the second transparent conductive film 4. After that, the metalfilm 3 formed under the second transparent conductive film 4 is etched.Accordingly, in patterning the second transparent conductive film 4 andthe metal film 3 using one resist pattern 5, the second transparentconductive film 4 does not project from the edge face of the metal film3 and the generation of the protruding portion can be prevented.Moreover, a multilayer thin film pattern of 2 layers or more can bepatterned using one resist pattern 5. By using the reflow of the resistusing an organic solvent, it is possible to transform the resist pattern5 largely in a short time.

Furthermore, in this embodiment, after etching the metal film 3, theresist pattern 5 is transformed again by the reflow of the resist usingan organic solvent to cover the edge face of a metal film 3. Then, thefirst transparent conductive film 2 formed under the metal film 3 isetched so that the retracting amount 21 of the first transparentconductive film 2 may become less than the retracting amount 31 of themetal film 3. This enables the metal film 3 not to project from the edgeface of the first transparent conductive film 2, thereby preventing fromgenerating the protruding portion. That is, by repeating thetransformation of the resist pattern 5 by the reflow of the resist usingan organic solvent and the etching, it is possible to prevent fromgenerating the protruding portion in patterning of the multilayer thinfilm pattern of 3 layers or more using one resist pattern 5. That is,the multilayer thin film pattern is formed stepwise. This embodiment isespecially preferable when the etch selectivity of the first transparentconductive film 2 over the second transparent conductive film 4 is low,½ or more and less than 2, preferably around 1. Moreover, it is possibleto pattern a multilayer thin film pattern of 3 layers or more using oneresist pattern 5. Therefore, a multilayer thin film pattern of desiredsectional shape can be obtained easily.

Second Embodiment

Next, a manufacturing method of a multilayer thin film pattern accordingto a second embodiment is explained. Since the manufacturing process ofthis embodiment is identical to that of the first embodiment except thetransformation method of the resist pattern 5, the explanation isomitted.

After etching the second transparent conductive film 4, in FIG. 3C, byexpansion of the resist size using RELACS (Resolution EnhancementLithography Assisted by Chemical Shrink), the entire resist pattern 5 istransformed to cover the edge face of the second transparent conductivefilm 4. Specifically, RELACS agent is applied over the resist pattern 5and heated. This makes an acid in the resist pattern 5 spread toinitiate a crosslinking reaction with the RELACS agent. That is, theRELACS agent near the resist pattern 5 changes and adheres to thesurface of the resist pattern 5 to form a thermally-hardened resinlayer. Subsequently, the RELACS agent of the unadhered part is removedby development, cleaning, or the like. This makes the RELACS agentadhere to the resist pattern 5 covering the edge face of the secondtransparent conductive film 4, and the entire resist pattern 5 expands.

Although the temperature of the heat applied to the RELACS agent isabout 100 to 120 degrees Celsius, the thickness of the layer adhering tothe resist pattern 5 can be controlled by adjusting this temperature.This enables to expand the resist pattern 5 size for about 0.5 to 1 μm.Since the film thickness of the second transparent conductive film 4 isabout 0.005 to 0.01 μm, the entire second transparent conductive film 4is sufficiently protected by the resist pattern 5 and the RELACS agentadhering to the resist pattern 5. The transformation of the resist usingthe RELACS agent is disclosed in Toyoshima, T. et al. “0.1 μm LevelContact Hole Pattern Formation with KrF Lithography by ResolutionEnhancement Lithography Assisted by Chemical Shrink (RELACS)”, IEDM,1998. pp. 333-336.

Moreover, similarly in FIG. 3E, the entire resist pattern 5 istransformed to cover the edge face of the metal film 3 by expansion ofthe resist size using RELACS.

As described above, in this embodiment, the resist pattern 5 istransformed by expansion of the resist size using RELACS after theetching process of the second transparent conductive film 4. Thus, aswith the first embodiment, in patterning the second transparentconductive film 4 and the metal film 3 using one resist pattern 5, thesecond transparent conductive film 4 does not project from the edge faceof the metal film 3 and the generation of the protruding portion can beprevented. Moreover, a multilayer thin film pattern of 2 layers or morecan be patterned using one resist pattern 5. Therefore, a multilayerthin film pattern of desired sectional shape can be obtained easily.

Furthermore, in this embodiment, after etching the metal film 3, theresist pattern 5 is transformed again by expansion of the resist sizeusing RELACS to cover the edge face of the metal film 3. Then, the firsttransparent conductive film 2 formed under the metal film 3 is etched.This enables the metal film 3 not to project from the edge face of thefirst transparent conductive film 2, thereby preventing from generatingthe protruding portion. That is, by repeating the transformation byexpansion of the resist size using RELACS and the etching, the sameeffect as the first embodiment can be created and it is possible toprevent from generating the protruding portion in patterning of themultilayer thin film pattern of 3 layers or more using one resistpattern 5. This embodiment is especially preferable when the etchselectivity of the first transparent conductive film 2 over the secondtransparent conductive film 4 is low, ½ or more and less than 2,preferably around 1. Moreover, it is possible to pattern a multilayerthin film pattern of 3 layers or more using one resist pattern 5.

Third Embodiment

Next, a manufacturing method of a multilayer thin film pattern accordingto a third embodiment is explained with reference to FIGS. 4A to 4G. Inthe manufacturing method of a pixel electrode of a transflective liquidcrystal display, multiphase exposure (multi-tone exposure) technique bya gray tone mask or a halftone mask may be used to form a transmissiveelectrode and a reflective electrode. By photolithography using themulti-tone exposure, a thick resist pattern 5 a in a reflective area anda thin resist pattern 5 b in a transmissive area of a pixel electrodecan be simultaneously formed. The transmissive electrode and thereflective electrode are formed using the thickness difference of theresist pattern 5. In this embodiment, an example is explained where themanufacturing method of a multilayer thin film pattern according to thepresent invention is incorporated when forming a transmissive electrodeand a reflective electrode by the photolithography using the multi-toneexposure.

FIGS. 4A to 4G are cross-sectional diagrams schematically showing themanufacturing process of the multilayer thin film pattern according tothe third embodiment. In FIGS. 4A to 4G, components identical to thosein FIGS. 3A to 3G are denoted by reference numerals identical to thosetherein and the differences are explained. Firstly, in FIGS. 4A to 4G aswith FIGS. 3A to 3G, the interlayer insulating film 1 such as an organicplanarizing film is formed above the TFT 20, the scanning signal line 13and the display signal line 14, as shown in FIGS. 2A and 2B. In FIGS. 4Ato 4G, the part below the interlayer insulating film 1 is omitted. InFIG. 4A, the first transparent conductive film 2, the metal film 3 to bea reflective electrode, and the second transparent conductive film 4 forpreventing image sticking are deposited in order. Then, the resistpattern 5 of desired plane shape is formed by a photolithography overthe second transparent conductive film 4. Here, using a gray tone masketc., the resist pattern 5 is formed so that the resist pattern 5 a inthe reflective area 8 is thicker than the resist pattern 5 b in thetransmissive area 9. That is, the thick film part of the resist pattern5 with different film thicknesses is to be the resist pattern 5 a andthe thin film part is to be the resist pattern 5 b.

Next, in FIG. 4B, the second transparent conductive film 4, the metalfilm 3 and the first transparent conductive film 2 are collectivelyetched. Or the second transparent conductive film 4, the metal film 3and the first transparent conductive film 2 may be separately etched. Insuch case, each film is patterned corresponding to the shape of theresist pattern 5 in order from the upper layer using an etchant whichselectively etches each film.

Then, the resist pattern 5 is ashed so that the resist pattern 5 may beremoved in the transmissive area 9 of the pixel electrode and remainonly in the reflective area 8, as shown in FIG. 4C. For example, ashingis performed in oxygen plasma. If the resist is removed until thesurface of the second transparent conductive film 4 is exposed in thetransmissive area 9, a resist pattern 5 c is shaped to cover thereflective area 8. This allows the thin resist pattern 5 b to be removedand the thick resist pattern 5 a to become thin but remain as the resistpattern 5 c. By this ashing, the resist pattern 5 c retracts from theedge face of the second transparent conductive film 4. After that, thesecond transparent conductive film 4 is selectively patterned byisotropic etching. By using isotropic etching, the second transparentconductive film 4 becomes smaller than the outer shape of the resistpattern 5 c and side etched as shown in FIG. 4D. At this time, it isdesirable that a retracting amount 42 of the second transparentconductive film 4 from the edge face of the resist pattern 5 c is morethan the retracting amount of the metal film 3 mentioned later. Here,only as a guide, the second transparent conductive film 4 is etcheduntil the retracting amount 42 is approximately more than twice the filmthickness of the metal film 3.

Next, the resist pattern 5 c is transformed by the reflow of the resistusing an organic solvent so that the resist pattern 5 covers the edgeface of the second transparent conductive film 4. This enables toprotect the entire second transparent conductive film 4 by the resistpattern 5 c, as shown in FIG. 4E. At this time, the edge faces of themetal film 3 and the first transparent conductive film 2 are not coveredwith the resist pattern 5 c but are exposed.

After that, in FIG. 4F, isotropic etching of the metal film 3 isselectively carried out. For example, wet etching can be used. At thistime, even a small amount of the remaining metal film 3 will have aharmful effect on product performance. Thus the metal film 3 must besufficiently over etched. Therefore, in consideration of the variationin etching and the homogeneity, the etching process corresponding about1.5 to the 2 times of the film thickness of the metal film 3 isperformed. At this time, a retracting amount (side etch amount) 32 ofthe metal film 3 from the edge face of the resist pattern 5 c is about1.5 to 2 times of the film thickness of the metal film 3. That is, theretracting amount 32 of the metal film 3 becomes smaller than theretracting amount 42 of the second transparent conductive film 4.Consequently, the bottom surface of the second transparent conductivefilm 4 is not exposed during the etching process of the metal film 3,thereby enabling to prevent from generating the protruding portion bythe second transparent conductive film 4.

Lastly, when the resist pattern 5 c is removed, the multilayer thin filmpattern with no protruding portion as shown in FIG. 4G can be obtained.That is, the multilayer thin film pattern is formed stepwise.

As described above, in this embodiment, a transmissive electrode and areflective electrode are formed by photolithography using multi-toneexposure. At this time, the second transparent conductive film 4 forpreventing image sticking is selectively etched using isotropic etchinguntil its retracting amount 42 becomes more than twice the filmthickness of the metal film 3 to be a reflective electrode. Then, aftertransforming the resist pattern 5 c by the reflow of the resist using anorganic solvent to cover the edge face of the second transparentconductive film 4, the metal film 3 is etched. Accordingly, inpatterning the second transparent conductive film 4 and the metal film 3using one resist pattern 5 c, the second transparent conductive film 4does not project from the edge face of the metal film 3 and thegeneration of the protruding portion can be prevented. Therefore, amultilayer thin film pattern of desired sectional shape can be obtainedeasily. Moreover, by using the reflow of the resist using an organicsolvent, it is possible to transform the resist pattern 5 c largely in ashort time.

Note that in this embodiment, an example is explained in which theresist pattern 5 c is transformed by the reflow of the resist using anorganic solvent in the process of transforming the resist pattern 5 c,however it is not limited to this. As with the second embodiment, theresist pattern 5 c may be transformed by expansion of the resist sizeusing RELACS. Then the same effect as the third embodiment can beachieved and in forming the multilayer thin film pattern using oneresist pattern 5 c, it is possible to prevent from generating theprotruding portion.

Fourth Embodiment

A manufacturing method of a multilayer thin film pattern according to afourth embodiment is explained with reference to FIGS. 5A to 5I. In thisembodiment, as with the third embodiment, another example is explainedwhere the manufacturing method of a multilayer thin film patternaccording to the present invention is incorporated when forming atransmissive electrode and a reflective electrode by thephotolithography using the multi-tone exposure. Since the manufacturingprocess of this embodiment is identical to that of the third embodimentexcluding a part of the process, the explanation is omitted. That is, inthe fourth embodiment, a different method from the third embodiment isused in the process corresponding to FIG. 4B of the third embodiment.

FIGS. 5A to 5I are cross-sectional diagrams schematically showing themanufacturing process of the multilayer thin film pattern according tothe fourth embodiment. Firstly, in FIGS. 5A to 5I, as with FIGS. 4A to4G, the interlayer insulating film 1 such as an organic planarizing filmis formed above the TFT 20, the scanning signal line 13 and the displaysignal line 14, as shown in FIGS. 2A and 2B. In FIGS. 5A to 5I, the partunder the interlayer insulating film 1 is omitted. In FIG. 5A as withFIG. 4A, the first transparent conductive film 2, the metal film 3 to bea reflective electrode, and the second transparent conductive film 4 forpreventing image sticking are deposited in order over the interlayerinsulating film 1. Then, furthermore, the resist pattern 5 of desiredplane shape is formed by photolithography thereover. Here, using a graytone mask etc., the resist pattern 5 is formed so that the resistpattern 5 a in the reflective area 8 is thicker than the resist pattern5 b in the transmissive area 9.

Next, in FIG. 5B, isotropic etching is selectively performed to thesecond transparent conductive film 4. For example, wet etching can beused. At this time, it is desirable that a retracting amount 43 of thesecond transparent conductive film 4 from the edge face of the resistpattern 5 is more than the retracting amount of the metal film 3mentioned later. For example, only as a guide, the second transparentconductive film 4 is etched until the retracting amount 43 isapproximately more than twice the film thickness of the metal film 3.Then, a part of the second transparent conductive film 4 is removed andthe metal film 3 is exposed outside of the resist pattern 5. Then, aswith the first embodiment, the resist pattern 5 is transformed by thereflow of the resist using an organic solvent so that the resist pattern5 covers the edge face of the second transparent conductive film 4. Thisenables to protect the entire second transparent conductive film 4 bythe resist pattern 5, as shown in FIG. 5C.

Subsequently, in FIG. 5D, isotropic etching of the metal film 3 isselectively carried out. For example, wet etching can be used. Even if asufficient etching which corresponds about 1.5 to 2 times of the filmthickness of the metal film 3 is performed at this time, a retractingamount 33 of the metal film 3 from the edge face of the resist pattern 5becomes less than the retracting amount 43 of the second transparentconductive film 4. After etching the metal film 3, the resist pattern 5is transformed again by the reflow of the resist using an organicsolvent to cover the edge face of the metal film 3. Then the secondtransparent conductive film 4 and the metal film 3 is protected entirelyby the resist pattern 5. Then, an etching process is performed to thefirst transparent conductive film 2. Here, the etching is performed sothat a retracting amount 23 of the first transparent conductive film 2from the edge face of the resist pattern 5 may become less than theretracting amount 33 of the metal film 3.

Note that in the process of FIG. 5D, after etching the metal film 3, theetching of the first transparent conductive film 2 is performed aftertransforming the resist pattern 5 to cover the edge face of the metalfilm 3. However, the first transparent conductive film 2 may be etchedwithout transforming the resist pattern 5. For example, for the etchingof the metal film 3 and the transparent conductive film 2, dry etchingmay be used to collectively etch them.

Thus, the edge face of the upper film is formed inside of the edge faceof the lower layer film and it is patterned to be the shape in which theupper film is not projected. Subsequently, the process after FIG. 5E isthe same as that of the third embodiment shown in FIGS. 4C to 4G. Thatis, in FIG. 5E, the resist pattern 5 is ashed to expose the secondtransparent conductive film 4 in the transmissive area 9. Then, as shownin FIGS. 5F to 5H, the second transparent conductive film 4 and themetal film 3 are etched. By removing the resist pattern 5 c lastly, themultilayer thin film pattern without the protruding portion can beobtained as shown in FIG. 5I. That is, the multilayer thin film patternis formed stepwise.

As described above, in this embodiment, the edge face of the secondtransparent conductive film 4, which is the upper layer, is protected bythe transformation of the resist pattern 5 also in the processcorresponding to FIG. 4B of the third embodiment. That is, when etchingthe lower layer film after etching the second transparent conductivefilm 4, the edge face of the second transparent conductive film 4 is tobe covered with the resist pattern 5. Then the protruding shape can becontrolled more certainly. Therefore, the multilayer thin film patternof desired sectional shape can be obtained easily. This embodiment isespecially preferable when the etch selectivity of the first transparentconductive film 2 and the second transparent conductive film 4 is low, ½or more and less than 2, preferably around 1.

Note that in this embodiment, an example is explained in which theresist pattern 5 is transformed by the reflow of the resist using anorganic solvent in the process of transforming the resist pattern 5,however it is not limited to this. As with the second embodiment, theresist pattern 5 may be transformed by expansion of the resist sizeusing RELACS. Then the same effect as the fourth embodiment can beachieved and in forming the multilayer thin film pattern using oneresist pattern 5, it is possible to prevent from generating theprotruding portion.

Fifth Embodiment

A manufacturing method of a multilayer thin film pattern according to afifth embodiment is explained with reference to FIGS. 6A to 6D. In thisembodiment, as with the third and the fourth embodiments, anotherexample is explained where the manufacturing method of a multilayer thinfilm pattern according to the present invention is incorporated whenforming a transmissive electrode and a reflective electrode by thephotolithography using the multi-tone exposure.

FIGS. 6A to 6D are cross-sectional diagrams schematically showing themanufacturing process of the multilayer thin film pattern according tothe fifth embodiment. In FIGS. 6A to 6D, components identical to thosein FIGS. 4A to 4G and FIGS. 5A to 5I are denoted by reference numeralsidentical to those therein and the differences are explained. Firstly,in FIGS. 6A to 6D, as with FIGS. 4A to 4G and FIGS. 5A to 5I, theinterlayer insulating film 1 such as an organic planarizing film isformed above the TFT 20, the scanning signal line 13 and the displaysignal line 14, as shown in FIGS. 2A and 2B. In FIGS. 6A to 6D, the partunder the interlayer insulating film 1 is omitted. In FIG. 6A of thisembodiment, the first transparent conductive film 2 to be a transmissiveelectrode and the metal film 3 to be a reflective electrode aredeposited in order over the interlayer insulating film 1. Then, theresist pattern 5 of desired plane shape is formed by a photolithographyover the metal film 3. Here, using multi-tone exposure technique, theresist pattern 5 is formed so that the resist pattern 5 a in thereflective area 8 is thicker than the resist pattern 5 b in thetransmissive area 9. Then, the resist pattern 5 with different filmthicknesses is formed over the metal film 3.

Next, in FIG. 6B, the metal film 3 and the first transparent conductivefilm 2 are etched using the resist pattern 5 as a mask. At this time, inorder to prevent abnormal electric discharge in ashing described later,the first transparent conductive film 2 is also etched. That is, thefirst transparent conductive film 2 is removed along with the metal film3 so that the interlayer insulating film 1 is exposed in the area notprovided with the resist pattern 5. Here, the metal film 3 and the firsttransparent conductive film 2 may be etched one by one separately or maybe etched collectively. When the metal film 3 and the first transparentconductive film 2 are etched collectively, the number of process stepcan be reduced, thereby improving the productivity. Then the metal film3 and the first transparent conductive film 2 are patterned to remainonly under the resist pattern 5.

Then, the resist pattern 5 is ashed so that the resist pattern 5 may beremoved in the transmissive area 9 and remain only in the reflectivearea 8 of the pixel electrode, as shown in FIG. 6C. Ashing is carriedout by plasma treatment in oxygen atmosphere. At this time, the firsttransparent conductive film 2 is not exposed to the surface in thisembodiment. That is, at the start of the ashing, the entire firsttransparent conductive film 2 is covered with the resist pattern 5 andit is possible to prevent faults such as abnormal electric dischargeduring ashing. When the resist is removed until the surface of the metalfilm 3 is exposed in the transmissive area 9, the resist pattern 5 c isformed to cover the reflective area 8. Then the thin resist pattern 5 bis removed and the thick resist pattern 5 a becomes thin but remains asthe resist pattern 5 c. By this ashing, the resist pattern 5 c retractsfrom the edge face of the metal film 3.

Subsequently, the metal film 3 is selectively etched with the resistpattern 5 c disposed thereon. Then the metal film 3 in the transmissivearea 9 is removed. Lastly, by removing the resist pattern 5 c, thestepwise multilayer thin film pattern as shown in FIG. 6D can beobtained.

As described above, in this embodiment, a transmissive electrode and areflective electrode are formed by the photolithography using multi-toneexposure. Before ashing the resist pattern 5 with different filmthicknesses, the first transparent conductive film 2 is also etched sothat the interlayer insulating film 1 is exposed. By such method, it ispossible to prevent from generating faults such as abnormal electricdischarge during ashing and also to obtain a multilayer thin filmpattern of desired shape easily. Moreover, patterns of a transmissiveelectrode area and a reflective electrode area can be formed in onephotolithography process, thereby improving the productivity.

Note that this embodiment can be combined with the first to the fourthembodiment. Specifically, when etching the metal film 3 and the firsttransparent conductive film 2 separately in FIG. 6B, it may be etched inthe following way. The metal film 3 is etched using the resist pattern 5having different film thicknesses as a mask. Then, by the reflow of theresist using an organic solvent or the expansion of the resist size byRELACS, the resist pattern 5 is transformed to cover the edge face ofthe metal film 3. Then, the first transparent conductive film 2 isetched. At this time, the first transparent conductive film 2 is etchedso that the retracting amount of the first transparent conductive film 2from the edge face of the resist pattern 5 becomes less than theretracting amount of the metal film 3. This enables to prevent fromgenerating the protruding portion. Moreover, in this embodiment, anexample of forming a multilayer thin film pattern including 2 layers ofconductive thin films having the metal film 3 stacked over the firsttransparent conductive film 2 is explained, however it is not limited tothis. It may be a case of forming a multilayer thin film having aninsulating film for example stacked to the conductive thin film over theinterlayer insulating film 1.

Sixth Embodiment

A manufacturing method of a multilayer thin film pattern according to asixth embodiment is explained with reference to FIGS. 7A to 7D. In thisembodiment, as with the third to the fifth embodiments, another exampleis explained where the manufacturing method of a multilayer thin filmpattern according to the present invention is incorporated when forminga transmissive electrode and a reflective electrode by thephotolithography using the multi-tone exposure.

FIGS. 7A to 7D are cross-sectional diagrams schematically showing themanufacturing process of the multilayer thin film pattern according tothe sixth embodiment. In FIGS. 7A to 7D, components identical to thosein FIGS. 4A to 4G, FIGS. 5A to 5I and FIGS. 6A to 6D are denoted byreference numerals identical to those therein and the differences areexplained. Firstly, in FIGS. 7A to 7D, as with FIGS. 4A to 4G, FIGS. 5Ato 5I and FIGS. 6A to 6D, the interlayer insulating film 1 such as anorganic planarizing film is formed above the TFT 20, the scanning signalline 13 and the display signal line 14, as shown in FIGS. 2A and 2B. InFIGS. 7A to 7D, the part under the interlayer insulating film 1 isomitted. In FIG. 7A of this embodiment, the first transparent conductivefilm 2 to be a transmissive electrode, the metal film 3 to be areflective electrode, and the second transparent conductive film 4 forpreventing image sticking are deposited in order over the interlayerinsulating film 1. Then, the resist pattern 5 of desired plane shape isformed by photolithography over the second transparent conductive film4. Using multi-tone exposure technique, the resist pattern 5 is formedso that the resist pattern 5 a in the reflective area 8 is thicker thanthe resist pattern 5 b in the transmissive area 9. Then, the resistpattern 5 with different film thicknesses is formed over the metal film3.

Next, in FIG. 7B, the second transparent conductive film 4, the metalfilm 3 and the first transparent conductive film 2 are etched using theresist pattern 5 as a mask. At this time, in order to prevent abnormalelectric discharge in ashing described later, the first transparentconductive film 2 is also etched. That is, the metal film 3 and thefirst transparent conductive film 2 are removed along with the secondtransparent conductive film 4 so that the interlayer insulating film 1is exposed in the area not provided with the resist pattern 5. Here, thesecond transparent conductive film 4, the metal film 3 and the firsttransparent conductive film 2 may be etched one by one separately or maybe etched collectively. By etching the second transparent conductivefilm 4, the metal film 3 and the first transparent conductive film 2collectively, the number of process step can be reduced, therebyimproving the productivity. Then the second transparent conductive film4, the metal film 3 and the first transparent conductive film 2 arepatterned to remain only under the resist pattern 5.

Then, the resist pattern 5 is ashed so that the resist pattern 5 may beremoved in the transmissive area 9 and remain only in the reflectivearea 8 of the pixel electrode, as shown in FIG. 7C. Ashing is carriedout by plasma treatment in oxygen atmosphere. At this time, the metalfilm 3 and the first transparent conductive film 2 are not exposed tothe surface in this embodiment. That is, at the start of the ashing, theentire first transparent conductive film 2 is covered with the resistpattern 5 and it is possible to prevent faults such as abnormal electricdischarge during ashing. When the resist is removed until the surface ofthe second transparent conductive film 4 is exposed in the transmissivearea 9, the resist pattern 5 c is shaped to cover the reflective area 8.Then the thin resist pattern 5 b is removed and the thick resist pattern5 a becomes thin but remains as the resist pattern 5 c. By this ashing,the resist pattern 5 c retracts from the edge face of the secondtransparent conductive film 4.

Subsequently, the second transparent conductive film 4 and the metalfilm 3 are selectively etched with the resist pattern 5 c disposedthereover. Then the second transparent conductive film 4 and the metalfilm 3 in the transmissive area 9 are removed. Lastly, by removing theresist pattern 5 c, the stepwise multilayer thin film pattern as shownin FIG. 7D can be obtained.

As described above, in this embodiment, a transmissive electrode and areflective electrode are formed by the photolithography using multi-toneexposure. Before ashing the resist pattern 5 with different filmthicknesses, the first transparent conductive film 2 is also etched sothat the interlayer insulating film 1 is exposed. By such method, it ispossible to prevent from generating faults such as abnormal electricdischarge during ashing and also to obtain a multilayer thin filmpattern of desired shape easily. Moreover, patterns of a transmissiveelectrode area and a reflective electrode area can be formed in onephotolithography process, thereby improving the productivity.

Note that this embodiment can be combined with the first to the fourthembodiments. More specifically, after ashing in FIG. 7C, the secondtransparent conductive film 4 and the metal film 3 may be etched usingthe method of FIGS. 4D to 4G according to the third embodiment, insteadof FIG. 7D. Moreover, after forming the resist pattern 5 with differentfilm thicknesses in FIG. 7A, the second transparent conductive film 4,the metal film 3 and the first transparent conductive film 2 may beetched using the method of FIGS. 5B to 5D, instead of FIG. 7B. Thisenables to prevent from generating the protruding portion. Furthermore,in this embodiment, an example is described that forms a multilayer thinfilm pattern including 3 layers of conductive thin films having thefirst transparent conductive film 2, the metal film 3 and the secondconductive film 4 stacked sequentially, however it is not limited tothis. That is, it may be a case of forming a multilayer thin filmpattern having 2 layers or more of thin films stacked to the conductivethin film over the interlayer insulating film 1. The thin film of 2layers or more formed over the conductive thin film may be an insulatinglayer.

In the first to the sixth embodiments, although the metal film 3 isexplained as a single layer formed of Al or an alloy mainly using Al asan example, it is not limited to this but may be a stacked layer of 2 ormore kinds of layers. For example, the metal film 3 may have thestructure in which Al, Ag or an alloy mainly using these materials isstacked over a layer of Cr, Mo, W, Ti or an alloy mainly using thesematerials. By using Al, Ag or an alloy mainly using these materials tothe upper layer side of the metal film 3, the optical property ofreflection improves. Moreover, by using Cr, Mo, W, Ti or an alloy mainlyusing these materials to the lower layer side of the metal film 3, anelectric connection with the first transparent conductive film 2 formedbelow the metal film 3 improves.

Furthermore, in order to improve optical property of reflection, anuneven portion may be formed to the interlayer insulating film 1 of thereflective area 8. The uneven portion of this interlayer insulating film1 is not illustrated in FIGS. 4A to 4G, FIGS. 5A to 5I, FIGS. 6A to 6Dand FIGS. 7A to 7D.

Although in this embodiment, the manufacturing method of a reflectiveelectrode and a transmissive electrode in a pixel electrode of atransflective liquid crystal display is explained as a preferred exampleof a multilayer thin film pattern and a display device, it is notlimited to this. Various multilayer thin film patterns and displaydevices can be formed by changing thin films for forming the multilayerthin film variously. For example, it may be a multilayer thin filmincluding a metal film for forming a source electrode and a drainelectrode of a TFT and a transparent conductive film made of ITO etc.formed thereover. Moreover, both of the reflow of the resist using anorganic solvent and the expansion of resist size by RELACS may becombined. That is, the first transformation of the resist pattern 5 maybe performed by the reflow of the resist using an organic solvent andthe second transformation of the resist pattern 5 may be performed bythe expansion of resist size using RELACS. Conversely, the firsttransformation of the resist pattern 5 may be performed by the expansionof resist size using RELACS and the second transformation of the resistpattern 5 may be performed by the reflow of the resist using an organicsolvent.

The above explanation is to describe the embodiments of the presentinvention and the present invention is not limited to the aboveembodiments. Moreover, those skilled in the art can change, add andchange each component of the above embodiments easily in the scope ofthe present invention.

From the invention thus described and it will be obvious that theembodiments of the invention may be varied in many ways. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention and all such modifications as would be obvious to one skilledin the art are intended for inclusion within the scope of the followingclaims.

1. A method of manufacturing a multilayer thin film pattern comprising:forming a first thin film over a substrate; forming a second thin filmover the first thin film; forming a resist pattern over the second thinfilm; etching the second thin film using the resist pattern as a mask;transforming the resist pattern using an organic solvent or a RELACSagent to cover an edge face of the etched second thin film; and etchingthe first thin film while the edge face of the second thin film iscovered with the resist pattern.
 2. The method according to claim 1,wherein the RELACS agent initiates a crosslinking reaction with theresist pattern by heat and forms a resin layer to a surface of theresist pattern.
 3. The method according to claim 1, wherein in theetching of the second thin film, the second thin film is etched toretract from an edge face of the resist pattern, and a retracting amountof the second thin film from the edge face of the resist pattern is morethan twice a thickness of the first thin film.
 4. The method accordingto claim 1, further comprising: transforming the resist pattern using anorganic solvent or a RELACS agent to cover an edge face of the etchedfirst thin film; and etching a third thin film provided under the firstthin film while the edge faces of the first and the second thin filmsare covered by the resist pattern.
 5. The method according to claim 4,wherein an etching selectivity of the second thin film over the thirdthin film in the etching of the third film is ½ or more and less than 2.6. The method according to claim 4, wherein in the etching of the firstthin film, the first thin film is etched to retract from the edge faceof the resist pattern, and a retracting amount of the first film fromthe edge face of the resist pattern is not less than a thickness of thethird thin film and also not more than a retracting amount of the secondthin film.
 7. The method according to claim 6, wherein in the etching ofthe third thin film, a retracting amount of the third thin film from theedge face of the resist pattern is not more than the retracting amountof the first thin film.
 8. The method according to claim 7, wherein thefirst thin film is a metal film including Al and the second and thethird thin films are transparent conductive films.
 9. The methodaccording to claim 1, wherein the formation of the resist patternincludes; forming a resist pattern having different film thicknesses bymulti-tone exposure; and ashing the resist pattern having different filmthicknesses to remove a thin film part of the resist pattern, wherein inthe etching of the second thin film, the second thin film is etchedusing the resist pattern without the thin film part as a mask.
 10. Themethod according to claim 1, wherein in the formation of the resistpattern, a resist pattern having different film thicknesses is formed bymulti-tone exposure, and in the etching of the second thin film, thesecond thin film is etched using the resist pattern having differentfilm thicknesses as a mask, the resist pattern having different filmthicknesses is ashed to remove a thin film part and the second thin filmis etched using the resist pattern without the thin film part as a mask.11. The method according to claim 9, further comprising: forming aninterlayer insulating film between the substrate and the first thinfilm; and etching the second and the first thin films using the resistpattern having different film thicknesses as a mask before ashing toexpose the interlayer insulating film.
 12. The method according to claim10, further comprising: forming an interlayer insulating film betweenthe substrate and the first thin film, wherein in the etching of thesecond thin film, the second and the first thin films are etched usingthe resist pattern having different film thicknesses as a mask beforeashing to expose the interlayer insulating film.
 13. A method ofmanufacturing a multilayer thin film pattern comprising: forming aninterlayer insulating film over a substrate; forming a conductive thinfilm over the interlayer insulating film; forming a thin film of onelayer or more over the conductive thin film; forming a resist patternhaving different film thicknesses by a multi-tone exposure over the thinfilm of one layer or more; etching the thin film of one layer or moreand the conductive thin film using the resist pattern having differentfilm thicknesses as a mask to expose the interlayer insulating film;ashing the resist pattern having different film thicknesses to remove athin film part of the resist pattern; and etching at least one layer ofthe thin film of one layer or more using the resist pattern without thethin film part as a mask.
 14. A method of manufacturing a display deviceusing the method according to claim
 1. 15. A method of manufacturing adisplay device using the method according to claim 13.